The lead acid battery is one of the most commonly used batteries in the world and is present in almost all petrol- and diesel-based motor vehicles. Lead acid batteries are also extensively used in the electric vehicle industry and as back-up energy systems for buildings such as hospitals. Due both to the toxicity of lead and its material value it is important that these batteries are recycled.
The recycling of lead batteries involves treatment of the paste and electrodes from the lead battery in order to separate the lead from the other battery components. This may involve physical separation techniques as well as chemical techniques such as hydrometallurgical processing, smelting and electrochemical processes. Electrochemical processes are preferred as they tend to result in extraction of lead in a purer form, with fewer impurities. Electrochemical processes also avoid the need for heating materials to very high temperatures, which is costly. Additional costs are also involved in the transport of spent lead acid batteries to centralised smelting facilities.
However, currently known electrochemical processes can be problematic as complex mixtures of chemicals are required to dissolve lead in a form suitable for treatment in an electrochemical cell. These chemicals are also very toxic as they are generally very concentrated acids and, thus, they are difficult to handle and require special safety precautions.
Lead(II) sulphate (PbSO4) and lead(IV) oxide (PbO2) are of vital importance in lead acid batteries. The charged lead acid battery has one electrode of Pb and one of PbO2, whilst the discharged battery has two electrodes of PbSO4. Thus, the ability to recycle PbSO4 and PbO2 from a spent lead acid battery is desirable.
Moreover, it is not only lead from lead acid batteries that require new methods for recycling. The emerging technologies of lead telluride thermoelectrics and lead perovskite solar cells show potential as key lead-based materials in the developing renewable energy landscape. These technologies, however, are often considered to be limited due to their reliance on toxic lead, and the subsequent risk of environmental damage when these devices reach the end of their working life. Currently there is no clear recycling technique for these materials. In the case of lead perovskite photovoltaics this is often considered to be one of the key limiting factors in their scale up and introduction to the marketplace. As lead is toxic the end of life issues for lead perovskite solar cells are pertinent. Three of the most commonly used and promising materials in the field of lead perovskite photovoltaics are CH3NH3PbI3 (MAPbI3), HC(NH2)2PbI3 (FAPbI3) and CH3NH3PbI3-XClX (MAPbI3-XClX). Through the safe and environmentally friendly recycling of lead perovskite solar cells, the issue surrounding the toxicity and pollution at the end of their working life can be overcome and these materials will be able to have a wider application in the marketplace.
Thus, there is a need for an improved process for recovering lead from the lead-based materials used in, for example, lead batteries and solar cells.